Guide to museum glazing: Fight fading
September 1, 2005
Running a museum is no day at the beach, but the experiences do have one thing in common: the need for advanced protection from ultraviolet rays.
Ultraviolet light constitutes the most damaging form of solar radiation. It damages more than just skin; it steals color from paints, paper, fabric and even plastic. As any curator or conservator can tell you, fading is cumulative and permanent.
“We spend a lot of time talking about UV damage,” says paper conservator Christine Young of Nashville, a consultant for museums, libraries and universities. “It is common. Most incidents of color fading are the result of UV light.”
The life and health of museum exhibits and works of art depend on protection from sunlight. With 27 years in art conservation, Young has seen UV technology improve considerably during her career. Today, a range of solutions exists, and they come with a variety of price tags.
To understand the options and benefits of UV protection, you must understand the science of sunlight.
Radiation from the sun contains ultraviolet, visible and infrared light. Shown on the graph at left, these three spectrums get defined by their wavelengths and measured in nanometers. One nano-meter equals one-billionth of a meter.
Visible light runs from 400-to-800 nanometers in wavelength. Any distortion of this spectrum will diminish or alter the appearance of a curator’s exhibit. Outside of that range, curators want to block as much solar radiation as possible.
Scientists define ultraviolet radiation as light in wavelengths of 295-to-380 nanometers. Invisible, it can be blocked completely without any detectable difference in lighting.
Ultraviolet light accounts for approximately 50 percent of fading damage. Although Young specializes in physical repairs and removing discoloration from artwork, there is no cure for UV damage. “Fading cannot be reversed,” she says. “Inks, paints, pastels—once they’ve faded, that’s it.”
An advanced UV glass coating that virtually eliminates UV radiation with minimal effect on the visible light spectrum becomes a most effective weapon against fading. The use of UV glass, in combination with humidity and temperature controls, offers powerful protection from fading. Architects, specifiers, curators, glass-shop owners and contract glaziers have three ways to employ UV glass in museums or galleries: frames, windows and light fixtures.
Framed artwork might be considered the easiest to protect because the glass lies immediately in front of a protected item. No light touches the piece without first passing through the UV-blocking glass.
“To me, archival framing must include UV glass or it is not archival,” says Jim Parrie, owner of Millennial Technologies & Consulting International of Covington, La. “If we protect the framed item from acid burn and adhesives but not UV light, then we have not done our jobs as framers.”
Parrie notes that low-quality printing materials have become more abundant, especially among upcoming artists who may not be able to afford premium materials. “We can restore many pieces of art when they have been damaged by acid due to improper framing. But when a piece fades due to UV light, it is gone forever.”
Standard glass effectively blocks UV radiation below 310 nanometers in wavelength. This leaves a wide band, 310-to-380 nanometers, unblocked. To help museum and gallery owners as well as artists and photographers eliminate this problem, Guardian Industries Corp. of Auburn Hills, Mich., developed a high-performance UV-blocking coating for the framing industry containing organic and inorganic materials and called Inspiration UV glass. Other glass manufacturers have competing products.
The UV-blocking technology in framed artwork is not just effective for displays, it prevents sun damage anywhere, including during storage or transport. “You can see damage after a single day in the sun,” points out Amie Geremia, registrar of the Frist Center for the Visual Arts in Nashville.
Two common methods enhance the UV-blocking performance of window glass. The first involves use of polymer films by physically applying the UV-blocking material to the glass surface following window fabrication. The advantage is that this technology can be applied to existing windows.
The Frist Center, like most major art museums, does not have any windows in display areas. “The only windows we have near exhibition areas are in the clerestory overlooking the lobby, and those windows are UV-filtered,” Geremia says.
The UV coating on the Frist Center windows was applied to existing windows during a 1999 renovation when the building was first transformed into a museum. The use of aftermarket window film can be an effective method of blocking UV radiation when window replacement is not an option, or in building designs such as the Frist Center where windows sit near the ceiling and do not provide light for viewing the artwork.
However, smaller museums, such as historic homes that have been renovated into art galleries, tend to have windows closer to exhibit spaces. In these environments, aftermarket films may have distinct disadvantages, such as a slight discoloration, reflectivity problems, wrinkles, bubbles and peeling. Also, aftermarket films may void manufacturers’ warranties on the windows.
Guardian and other manufacturers offer glass surface coatings for advanced UV protection. These coatings cannot wrinkle or peel, do not create any distortion and can be cleaned with most common glass cleansers. Plus, coatings such as ClimaGuard SPF are scratch-resistant and can be resized with standard glass-cutting tools. However, the coating must be applied during glass fabrication, not on site.
Indoor light from artificial sources contains the same three spectrums as sunlight: ultraviolet, visible and infrared. However, artificial light remains far less intense than solar radiation. Fading caused by sunlight can also be caused by artificial light, especially fluorescent lights, but to a much smaller degree. UV coatings designed to minimize damage from sunlight also will prevent damage from artificial sources.
Artwork behind a frame with UV glass is, of course, largely protected from artificial light. You can provide additional protection with UV-blocking light covers, now available in glass or Plexiglass.
What causes fading?
Although generally defined as a simple loss of color, “fading” actually comprises a complex chemical reaction that allows sunlight to break apart the bonds in organic molecules.
Different materials can handle different levels of UV light before they break down. For example, ethanol, used in paints, paint thinners and finishes, tends to breakdown if exposed to UV light below 311 nanometers in wavelength. The plastics component methyl chloride has a threshold of 340 nanometers, and the paint component ethyl chloride breaks down rapidly in UV light less than 353 nanometers. As these materials break down, color rapidly disappears.
The most advanced UV coating technology on the market today can block 99 percent of UV light below 380 nanometers in wavelength. Compared to traditional glass and as shown on the graph on p. 75, UV glass virtually eliminates most of the ultraviolet energy that would otherwise devastate artwork.
To demonstrate how effective UV glass can be in real-world applications, Guardian researchers tested a framed photograph printed on high-quality, brand-name paper, subjecting it to the equivalent of 10 years of perpendicular 365-nanometer UV radiation. As shown above, the right side of the photograph was protected by UV glass while the left side was under ordinary glass. The unprotected half lost its intense red pigments and faded to pale yellow. The other half remains vibrant.
You may ask yourself, “What about infrared light?”
Infrared light, more than 800 nanometers in wavelength, would be responsible for approximately 25 percent of fading if museum and gallery displays were left unprotected. Fortunately, the heat, or infrared, resistance of glass has long been of interest to glass manufacturers who want to minimize heat loss and excessive heat gain through windows. Low-emissivity coatings have become commonplace and effective at significantly reducing the amount of infrared light penetrating a window. Combining a low-emissivity coating with advanced UV-blocking coating achieves maximum protection from all wavelengths of invisible light.
The future of UV protection
UV glass is rapidly becoming commonplace in consumer products. In the coming months, UV-blocking windows will hit the marketplace for homeowners and builders who have become increasingly concerned about the harmful effects of UV light.
Nearly all windows sold today contain a double-pane insulating glass unit and more than half include a low-e coating. Combining a UV-blocking coating with a low-e coating will reduce UV penetration from the current standard of 56.9 percent for a standard clear glass window to less than 1 percent. In other words, almost all ultraviolet radiation will be blocked from entering the building at the source, the window. This is important for museums and galleries because it will protect more than just artwork.
Carpeting, fabrics and furniture are all susceptible to the chemical breakdown caused by ultraviolet light. Museums curators will see the same advantages that homeowners demand: better protection for all vulnerable colors.
“Homeowners want to protect their investments, whether it’s artwork or furniture,” Parrie says. “If consumers understand the value of UV protection and are willing to pay for it, then a museum definitely should.”
Testing is currently underway to determine the health benefits of UV-blocking windows. As the quality and availability of UV glass continues to grow, the marketplace for this technology is destined to spread from museums to homes to businesses and beyond.